{*******************************************************************************

        Jean-Pierre LESUEUR (@DarkCoderSc)
        www.phrozen.io
        SLAE32 - Assignment N°7 Crypters.
        Compiled with Lazarus.

*******************************************************************************}

unit UntCRC32;

{$mode objfpc}{$H+}

interface

uses SysUtils;

{
    Lookup Table

    Ref: https://wiki.osdev.org/CRC32
}
const poly8_lookup : array[0..256-1] of cardinal = (
        $00000000, $77073096, $EE0E612C, $990951BA,
        $076DC419, $706AF48F, $E963A535, $9E6495A3,
        $0EDB8832, $79DCB8A4, $E0D5E91E, $97D2D988,
        $09B64C2B, $7EB17CBD, $E7B82D07, $90BF1D91,
        $1DB71064, $6AB020F2, $F3B97148, $84BE41DE,
        $1ADAD47D, $6DDDE4EB, $F4D4B551, $83D385C7,
        $136C9856, $646BA8C0, $FD62F97A, $8A65C9EC,
        $14015C4F, $63066CD9, $FA0F3D63, $8D080DF5,
        $3B6E20C8, $4C69105E, $D56041E4, $A2677172,
        $3C03E4D1, $4B04D447, $D20D85FD, $A50AB56B,
        $35B5A8FA, $42B2986C, $DBBBC9D6, $ACBCF940,
        $32D86CE3, $45DF5C75, $DCD60DCF, $ABD13D59,
        $26D930AC, $51DE003A, $C8D75180, $BFD06116,
        $21B4F4B5, $56B3C423, $CFBA9599, $B8BDA50F,
        $2802B89E, $5F058808, $C60CD9B2, $B10BE924,
        $2F6F7C87, $58684C11, $C1611DAB, $B6662D3D,
        $76DC4190, $01DB7106, $98D220BC, $EFD5102A,
        $71B18589, $06B6B51F, $9FBFE4A5, $E8B8D433,
        $7807C9A2, $0F00F934, $9609A88E, $E10E9818,
        $7F6A0DBB, $086D3D2D, $91646C97, $E6635C01,
        $6B6B51F4, $1C6C6162, $856530D8, $F262004E,
        $6C0695ED, $1B01A57B, $8208F4C1, $F50FC457,
        $65B0D9C6, $12B7E950, $8BBEB8EA, $FCB9887C,
        $62DD1DDF, $15DA2D49, $8CD37CF3, $FBD44C65,
        $4DB26158, $3AB551CE, $A3BC0074, $D4BB30E2,
        $4ADFA541, $3DD895D7, $A4D1C46D, $D3D6F4FB,
        $4369E96A, $346ED9FC, $AD678846, $DA60B8D0,
        $44042D73, $33031DE5, $AA0A4C5F, $DD0D7CC9,
        $5005713C, $270241AA, $BE0B1010, $C90C2086,
        $5768B525, $206F85B3, $B966D409, $CE61E49F,
        $5EDEF90E, $29D9C998, $B0D09822, $C7D7A8B4,
        $59B33D17, $2EB40D81, $B7BD5C3B, $C0BA6CAD,
        $EDB88320, $9ABFB3B6, $03B6E20C, $74B1D29A,
        $EAD54739, $9DD277AF, $04DB2615, $73DC1683,
        $E3630B12, $94643B84, $0D6D6A3E, $7A6A5AA8,
        $E40ECF0B, $9309FF9D, $0A00AE27, $7D079EB1,
        $F00F9344, $8708A3D2, $1E01F268, $6906C2FE,
        $F762575D, $806567CB, $196C3671, $6E6B06E7,
        $FED41B76, $89D32BE0, $10DA7A5A, $67DD4ACC,
        $F9B9DF6F, $8EBEEFF9, $17B7BE43, $60B08ED5,
        $D6D6A3E8, $A1D1937E, $38D8C2C4, $4FDFF252,
        $D1BB67F1, $A6BC5767, $3FB506DD, $48B2364B,
        $D80D2BDA, $AF0A1B4C, $36034AF6, $41047A60,
        $DF60EFC3, $A867DF55, $316E8EEF, $4669BE79,
        $CB61B38C, $BC66831A, $256FD2A0, $5268E236,
        $CC0C7795, $BB0B4703, $220216B9, $5505262F,
        $C5BA3BBE, $B2BD0B28, $2BB45A92, $5CB36A04,
        $C2D7FFA7, $B5D0CF31, $2CD99E8B, $5BDEAE1D,
        $9B64C2B0, $EC63F226, $756AA39C, $026D930A,
        $9C0906A9, $EB0E363F, $72076785, $05005713,
        $95BF4A82, $E2B87A14, $7BB12BAE, $0CB61B38,
        $92D28E9B, $E5D5BE0D, $7CDCEFB7, $0BDBDF21,
        $86D3D2D4, $F1D4E242, $68DDB3F8, $1FDA836E,
        $81BE16CD, $F6B9265B, $6FB077E1, $18B74777,
        $88085AE6, $FF0F6A70, $66063BCA, $11010B5C,
        $8F659EFF, $F862AE69, $616BFFD3, $166CCF45,
        $A00AE278, $D70DD2EE, $4E048354, $3903B3C2,
        $A7672661, $D06016F7, $4969474D, $3E6E77DB,
        $AED16A4A, $D9D65ADC, $40DF0B66, $37D83BF0,
        $A9BCAE53, $DEBB9EC5, $47B2CF7F, $30B5FFE9,
        $BDBDF21C, $CABAC28A, $53B39330, $24B4A3A6,
        $BAD03605, $CDD70693, $54DE5729, $23D967BF,
        $B3667A2E, $C4614AB8, $5D681B02, $2A6F2B94,
        $B40BBE37, $C30C8EA1, $5A05DF1B, $2D02EF8D
);

function CRC32(pBuffer : Pointer; ABufferSize : Cardinal) : Cardinal; overload;
function CRC32h(pBuffer : Pointer; ABufferSize : Cardinal) : String; overload;
function CRC32(AString : String) : Cardinal; overload;
function CRC32h(AString : String) : String; overload;

implementation

{-------------------------------------------------------------------------------
    CRC32 Memory

    Ref: https://en.wikipedia.org/wiki/Cyclic_redundancy_check
-------------------------------------------------------------------------------}
function CRC32(pBuffer : Pointer; ABufferSize : Cardinal) : Cardinal;
var i            : Integer;
    nLookupIndex : Integer;
begin
    result := 0;
    if (NOT Assigned(pBuffer)) or (ABufferSize = 0) then
        Exit();
    ///

    result := $ffffffff;
    for i := 0 to ABufferSize -1 do begin
        nLookupIndex := (result xor PByte(Cardinal(pBuffer) + i)^) and $000000ff;

        result := (result shr 8) xor poly8_lookup[nLookupIndex];
    end;

    ///
    result := result xor $ffffffff;
end;

function CRC32h(pBuffer : Pointer; ABufferSize : Cardinal) : String;
var ACRC32 : Cardinal;
begin
    result := '';
    ///

    ACRC32 := CRC32(pBuffer, ABufferSize);

    if (ACRC32 <> 0) then
        result := IntToHex(ACRC32, 8);
end;

{-------------------------------------------------------------------------------
    String To CRC32
-------------------------------------------------------------------------------}
function CRC32(AString : String) : Cardinal;
begin
    result := CRC32(@AString[1], (Length(AString) * SizeOf(Char)));
end;

function CRC32h(AString : String) : String;
begin
    result := CRC32h(@AString[1], (Length(AString) * SizeOf(Char)));
end;

end.
